1. Field of the Invention
This invention relates to photographic developing compositions, photographic developing processes, and photographic silver halide elements and emulsions with incorporated developing agents. In particular, the invention relates to certain oxa- and thiadiazole compounds as photographic silver halide developing agents.
2. Description of the Prior Art
Oxa- and thiadiazole compounds, including oxa- and thiadiazoles bearing appended amino or nitrogen-linked moieties, are well known for use in photographic processes. For example, in U.S. Pat. No. 3,306,746 (issued Feb. 28, 1967 to Moses A. Schwartz) sulfa substituted heterocyclic compounds, such as 2-methyl-5-sulfa-1,3,4-thiadiazole, are disclosed for use in developer compositions in conjunction with conventional developing agents. In U.S. Pat. No. 3,212,892 (issued Oct. 19, 1965 to Anita von Konig et al) a secondary amino mercapto thiadiazole is disclosed for use in preventing deposition of silver sludge on photographic elements as a consequence of developing with conventional developing agents. The thiadiazole disclosed, however, is said to have no influence on the photographic materials being processed in the disclosed developing solutions (see U.S. Pat. No. 3,212,892 supra at col. 1, lines 36-44). Mercapto thiadiazole compounds similar to those in U.S. Pat. No. 3,212,892, and mercapto oxadiazoles are the subject of British Patent 1,293,622 (published Oct. 18, 1972 and issued to Agfa-Gevaert Aktiengesellschaft) in which these compounds are said to stabilize silver images when employed in development baths in rapid photographic reproduction processes. Furthermore, a primary amino mercapto thiadiazole is disclosed in U.S. Pat. No. 3,020,155 (issued Feb. 6, 1962 to E. C. Yacket et al) for use in a diffusion transfer element to obtain black reproductions. The disclosed thiadiazole is said to be introducible into the diffusion transfer element by inclusion in a conventional developing solution.
The compounds discussed in the above patents, aside from being oxa- or thiadiazoles, bear only a single amino or nitrogen-linked moiety appended to the heterocyclic nucleus. In each instance, moreover, the disclosed compounds are employed only in conjunction with conventional developing agents. There is no suggestion in these patents that bis (secondary amino) thia- or oxadiazole compounds may be employed as photographic silver halide developing agents.
Further, in U.S. Pat. No. 2,915,395 (issued Dec. 1, 1959 to S. P. Popeck et al) 3,5-diureido-1,2,4-triazole and a water-soluble disulfonate thereof are disclosed as development accelerators for incorporation in a silver halide photographic emulsion in combination with a nitrobenzotriazole antifogging agent. This use of a dureido triazole, of course, does not suggest the use of bis(secondary amino) oxa- or thiadiazoles as photographic silver halide developing agents.
In the photographic field, there is continuing research underway to find new developing agents with broad utility. Not infrequently, compounds capable of reducing exposed silver salts are found, but for one reason or another their utility is severely limited. For example, the oxidized species of such compounds may be colored, causing undesirable "stain" in a photographic element processed with such compounds. Or, while desirably employed in a developer solution, a developing agent can be useless as an incorporated developing agent (i.e., one incorporated in a photographic emulsion) since it may be unstable in the emulsion. An incorporated developing agent may also cause spontaneous fogging of the silver salts, or may be lost by oxidation. Furthermore, even though compounds may exist which appear to avoid these problems, they may not have sufficient aqueous solubility or solubility in water-miscible solvents to enjoy commercial acceptance. Accordingly, developing agents having such universal applications are highly desirable.